Question

我制作了以下代码来通过字典循环键

favourite_languages = {
    'jen':'python',
    'sarah':'c',
    'edward':'ruby',
    'phil':'python'
    }

friends = ['sarah', 'phil']
for name in favourite_languages.keys():
    print(name.title())

if name in friends:
    print(" Hi " + name.title() + ", I see your favourite language is " +
          favourite_languages[name].title() + "!")

产生的输出是

Jen
Sarah
Edward
Phil
 Hi Phil, I see your favourite language is Python!

然而，我期待以下内容：

Jen
Sarah
 Hi Sarah, I see your favourite language is C!
Edward
Phil
 Hi Phil, I see your favourite language is Python!

为什么莎拉没有出现在输出中？

Answer 1

解决方案是，如果条件在循环内，你只需要移动你。

favourite_languages = {
    'jen':'python',
    'sarah':'c',
    'edward':'ruby',
    'phil':'python'
    }

friends = ['sarah', 'phil']
for name in favourite_languages.keys():
    print(name.title())

    if name in friends:
        print(" Hi " + name.title() + ", I see your favourite language is " +
              favourite_languages[name].title() + "!")

输出：

Sarah
 Hi Sarah, I see your favourite language is C!
Edward
Jen
Phil
 Hi Phil, I see your favourite language is Python!

Answer 2

您需要将if语句移动到循环中。在当前状态下，它位于外部，因此只能访问name所采用的最后一个值。

此外，我建议您将friends存储为一组，以便快速有效地查找。

In [193]: favourite_languages = {
     ...:     'jen':'python',
     ...:     'sarah':'c',
     ...:     'edward':'ruby',
     ...:     'phil':'python'
     ...:     }
     ...: 
     ...: friends = {'sarah', 'phil'}
     ...: for name in favourite_languages.keys():
     ...:     print(name.title())
     ...: 
     ...:     if name in friends:
     ...:         print(" Hi " + name.title() + ", I see your favourite language is " +
     ...:               favourite_languages[name].title() + "!") 
     ...:           
Phil
 Hi Phil, I see your favourite language is Python!
Jen
Edward
Sarah
 Hi Sarah, I see your favourite language is C!

集合具有恒定时间(O(1))查找，而列表是线性(O(n))。对于您的特定用例而言，这可能并不重要，但是设置确实会产生大量数据。

作为进一步的改进，您不需要调用dict.keys()，因为这会创建循环键的列表以进行迭代，这有点浪费。同样的事情可以通过以下方式实现：

for name in favourite_languages:

这更简单，更有效率。

Answer 3

if语句中的memory.limit(size=10000000000024)变量在循环后设置为name的最后一个值，而if语句只执行一次。

我认为你想缩进if语句（并打印），以便它在循环的每次迭代中执行

Answer 4

您没有循环遍历name变量。

当您的代码到达if name in friends时，name中存储的值为phil。

您可以再次遍历名称（这会产生稍微不同的结果），或者为代码添加缩进。

favourite_languages = {
'jen':'python',
'sarah':'c',
'edward':'ruby',
'phil':'python'
}

friends = ['sarah', 'phil']
for name in favourite_languages.keys():
    print(name.title())

    if name in friends:
        print(" Hi " + name.title() + ", I see your favourite language is " +
              favourite_languages[name].title() + "!")

Answer 5

将您的def get_answer c ? self.b = nil : b end块再缩进一层。

if

Answer 6

您需要缩进if name in friends:

favourite_languages = {
    'jen':'python',
    'sarah':'c',
    'edward':'ruby',
    'phil':'python'
    }

friends = ['sarah', 'phil']
for name in favourite_languages.keys():
    print(name.title())

    if name in friends:
        print(" Hi " + name.title() + ", I see your favourite language is " +
          favourite_languages[name].title() + "!")

Answer 7

只需将if语句移至for循环中。

Python Dictionary Loop不起作用

7 个答案: